Lithographic apparatus, device manufacturing method, and device manufactured thereby

ABSTRACT

A lithographic apparatus according to one embodiment of the invention includes an image sensing device configured and arranged to measure a pattern in a patterned beam of radiation. The image sensing device comprises a slab on which at least two sensors are formed. The sensors are sensitive to radiation of the beam and are arranged on a first side of the slab. A film that is non-transparent to radiation of the beam is provided at the first side over the sensors. The film includes a patterned segment above each sensor.

This application is a Divisional Application of U.S. application Ser.No. 10/164,706, filed Jun. 10, 2002 now U.S. Pat. No. 6,747,282, thecontents of which are incorporated herein by reference, and which claimspriority to EP 01202274.5 filed Jun. 13, 2001.

FIELD OF THE INVENTION

The present invention relates to lithographic projection methods,systems, and apparatus and to products of such methods, systems, andapparatus.

BACKGROUND

The term “patterning structure” as here employed should be broadlyinterpreted as referring to any structure or field that may be used toendow an incoming radiation beam with a patterned cross-section,corresponding to a pattern that is to be created in a target portion ofa substrate; the term “light valve” can also be used in this context.Generally, such a pattern will correspond to a particular functionallayer in a device being created in the target portion, such as anintegrated circuit or other device (see below). Examples of suchpatterning structure include:

A mask. The concept of a mask is well known in lithography, and itincludes mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. Placementof such a mask in the radiation beam causes selective transmission (inthe case of a transmissive mask) or reflection (in the case of areflective mask) of the radiation impinging on the mask, according tothe pattern on the mask. In the case of a mask, the support structurewill generally be a mask table, which ensures that the mask can be heldat a desired position in the incoming radiation beam, and that it can bemoved relative to the beam if so desired.

A programmable mirror array. One example of such a device is amatrix-addressable surface having a viscoelastic control layer and areflective surface. The basic principle behind such an apparatus is that(for example) addressed areas of the reflective surface reflect incidentlight as diffracted light, whereas unaddressed areas reflect incidentlight as undiffracted light. Using an appropriate filter, the saidundiffracted light can be filtered out of the reflected beam, leavingonly the diffracted light behind; in this manner, the beam becomespatterned according to the addressing pattern of the matrix-addressablesurface. An alternative embodiment of a programmable mirror arrayemploys a matrix arrangement of very small (possibly microscopic)mirrors, each of which can be individually tilted about an axis byapplying a suitable localized electric field, or by employingpiezoelectric actuation means. For example, the mirrors may bematrix-addressable, such that addressed mirrors will reflect an incomingradiation beam in a different direction to unaddressed mirrors; in thismanner, the reflected beam is patterned according to the addressingpattern of the matrix-addressable mirrors. The required matrixaddressing can be performed using suitable electronic means. In both ofthe situations described hereabove, the patterning structure cancomprise one or more programmable mirror arrays. More information onmirror arrays as here referred to can be gleaned, for example, from U.S.Pat. No. 5,296,891 and No. 5,523,193, and PCT patent applications WO98/38597 and WO 98/33096. In the case of a programmable mirror array,the said support structure may be embodied as a frame or table, forexample, which may be fixed or movable as required.

A programmable LCD array. An example of such a construction is given inU.S. Pat. No. 5,229,872. As above, the support structure in this casemay be embodied as a frame or table, for example, which may be fixed ormovable as required.

For purposes of simplicity, the rest of this text may, at certainlocations, specifically direct itself to examples involving a mask andmask table; however, the general principles discussed in such instancesshould be seen in the broader context of the patterning structure ashereabove set forth.

Lithographic projection apparatus can be used, for example, in themanufacture of integrated circuits (ICs). In such a case, the patterningstructure may generate a circuit pattern corresponding to an individuallayer of the IC, and this pattern can be imaged onto a target portion(e.g. comprising one or more dies) on a substrate (e.g. a wafer ofsilicon or other semiconductor material) that has been coated with alayer of radiation-sensitive material (resist). In general, a singlewafer will contain a whole network of adjacent target portions that aresuccessively irradiated via the projection system, one at a time. Incurrent apparatus, employing patterning by a mask on a mask table, adistinction can be made between two different types of machine. In onetype of lithographic projection apparatus, each target portion isirradiated by exposing the entire mask pattern onto the target portionat once; such an apparatus is commonly referred to as a wafer stepper.In an alternative apparatus—commonly referred to as a step-and-scanapparatus—each target portion is irradiated by progressively scanningthe mask pattern under the projection beam in a given referencedirection (the “scanning” direction) while synchronously scanning thesubstrate table parallel or anti-parallel to this direction; since, ingeneral, the projection system will have a magnification factor M(generally <1), the speed V at which the substrate table is scanned willbe a factor M times that at which the mask table is scanned. Moreinformation with regard to lithographic devices as here described can begleaned, for example, from U.S. Pat. No. 6,046,792.

In a manufacturing process using a lithographic projection apparatus, apattern (e.g. in a mask) is imaged onto a substrate that is at leastpartially covered by a layer of radiation-sensitive material (resist).Prior to this imaging step, the substrate may undergo variousprocedures, such as priming, resist coating and a soft bake. Afterexposure, the substrate may be subjected to other procedures, such as apost-exposure bake (PEB), development, a hard bake andmeasurement/inspection of the imaged features. This array of proceduresis used as a basis to pattern an individual layer of a device, e.g. anIC. Such a patterned layer may then undergo various processes such asetching, ion-implantation (doping), metallization, oxidation,chemo-mechanical polishing, etc., all intended to finish off anindividual layer. If several layers are required, then the wholeprocedure, or a variant thereof, will have to be repeated for each newlayer. Eventually, an array of devices will be present on the substrate(wafer). These devices are then separated from one another by atechnique such as dicing or sawing, whence the individual devices can bemounted on a carrier, connected to pins, etc. Further informationregarding such processes can be obtained, for example, from the book“Microchip Fabrication: A Practical Guide to Semiconductor Processing”,Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN0-07-067250-4.

For the sake of simplicity, the projection system may hereinafter bereferred to as the “lens”; however, this term should be broadlyinterpreted as encompassing various types of projection system,including refractive optics, reflective optics, and catadioptricsystems, for example. The radiation system may also include componentsoperating according to any of these design types for directing, shapingor controlling the projection beam of radiation, and such components mayalso be referred to below, collectively or singularly, as a “lens”.Further, the lithographic apparatus may be of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Dual stage lithographicapparatus are described, for example, in U.S. Pat. No. 5,969,441 and PCTpatent application WO 98/40791.

An image sensing device, which may be mounted on the substrate table, isused to measure a mark pattern present in the patterning structure so asto determine a plane of best focus of the lens, to determine lensaberrations, and to align the substrate table with respect to thepatterning structure. Presently, an image sensor comprises severalseparate sensors located behind detection structures that may take theform of gratings. Generally, one type of detection structure is presentabove a single sensor, and several detection structures and respectivesensors are required to determine the pattern characteristics asdescribed. The detection structures may generally be processed in asingle plate behind which the separate sensors are located.

The use of separate sensors requires a rather large distance betweenneighboring sensors. This requirement makes an imaging device thatincludes several complementary sensors and detection structures ratherlarge, which may cause a problem when a narrow illumination field isbeing used and which may also limit measurements at the edge of theimage field. Further, the present structured plate above the sensors maybe somewhat unflat due to a mechanical treatment to make the detectionstructures and to mount it above the separate sensors. This shortcomingmay cause capturing problems, since not all detection structures may bein best focus simultaneously.

Especially when short-wavelength radiation (such as extreme ultraviolet(EUV) radiation in the range of 10 to 15 nm) is used, the illuminationfield will become narrower and the requirements for the flatness of theplane in which the detection structures are present will become morestringent. Shorter wavelength radiation also requires the plate in whichthe detection structures are present to be thinner and the line widthsof the detection structures to be smaller. A very flat image sensingplate is also required for a level sensor that may be used to determineheight and tilt of the substrate table.

SUMMARY

As described herein, embodiments of the present invention may include animage-sensing device of which separate sensors and respective detectionstructures are located very close so as to present limited dimensions.

Embodiments of the present invention may also include an image-sensingdevice of which a front surface is very flat such that the variousdetection structures are arranged in one well-defined plane.

Embodiments of the present invention may further include animage-sensing device of which dimensions are very insensitive totemperature variations.

One embodiment of the invention is a lithographic projection apparatusthat is configured and arranged to image a pattern onto a substrate thatis at least partially covered by a layer of radiation-sensitivematerial. This apparatus includes a radiation system configured andarranged to provide a projection beam of radiation, a support structureconfigured and arranged to support a patterning structure that serves toproduce a desired pattern in the projection beam, a substrate tableconfigured and arranged to hold the substrate, and a projection systemconfigured and arranged to project the patterned projection beam onto atarget portion of the substrate.

The apparatus also includes an image sensing device configured andarranged to measure a pattern in the patterned projection beam. Theimage sensing device includes a slab and a radiation-sensitive sensorarranged on a first side of the slab. The sensor is an integral part ofsaid slab and is sensitive to the radiation of the projection beam.

The image sensing device also includes a film of a material that isnon-transparent to the radiation of the projection beam. This film isprovided on the first side of the slab over the sensor and includes oneor more patterned segments above the sensor to selectively passradiation of the projection beam to the sensor.

The apparatus also includes an intermediate plate made from a materialhaving a thermal expansion coefficient below approximately 12×10⁻⁶K⁻¹.The slab is mounted such that a surface opposite to its first side facesa slab-bearing surface of the intermediate plate.

For at least some applications of such an apparatus, one or more sensorsmay be made accurately in a slab of material, preferably a wafer ofsemiconductor material, such as a silicon wafer, using semiconductormanufacturing techniques, and the slab preferably being polished to havevery flat surfaces. Mechanical stability and a very good overallflatness is then achieved by mounting the slab onto the intermediateplate, which is also preferably polished to have a very flatslab-bearing surface. Direct bonding of slab to an intermediate provesto be a very strong and efficient means of attachment. Electricalconnections to the sensors may now advantageously be provided throughslab and intermediate plate to further electronics.

Another embodiment of the invention is a lithographic projectionapparatus that is configured and arranged to image a pattern onto asubstrate that is at least partially covered by a layer ofradiation-sensitive material. This apparatus includes a radiation systemconfigured and arranged to provide a projection beam of radiation, asupport structure configured and arranged to support a patterningstructure that serves to produce a desired pattern in the projectionbeam, a substrate table configured and arranged to hold the substrate,and a projection system configured and arranged to project the patternedprojection beam onto a target portion of the substrate.

The apparatus also includes an image sensing device configured andarranged to measure a pattern in the patterned projection beam. Theimage sensing device includes a slab and at least tworadiation-sensitive sensors arranged on a first side of the slab. Thesensors are an integral part of said slab and are sensitive to theradiation of the projection beam.

The image sensing device also includes a film of a material that isnon-transparent to the radiation of the projection beam. This film isprovided on the first side of the slab over the sensors and includes oneor more patterned segments above the sensors to selectively passradiation of the projection beam to the sensors.

In this apparatus, at least one of the sensors is configured andarranged to measure an intensity of an unpatterned area in across-section of the patterned projection beam, and at least another oneof said sensors is configured and arranged to measure an intensity of apatterned area neighboring the unpatterned area in the cross-section ofthe patterned projection beam. Each of the patterned segments above thesensors comprises a plurality of transmissive structures, a width of thetransmissive structures within each patterned segment being at leastsubstantially equal.

Another embodiment of the invention is a device manufacturing methodthat includes using a radiation system to provide a projection beam ofradiation; using patterning structure to endow the projection beam witha pattern in its cross-section; and projecting the patterned beam ofradiation onto a target portion of a layer of radiation-sensitivematerial that at least partially covers a substrate. This method alsoincludes measuring a pattern in the patterned projection beam using animage sensing device that includes a slab; a radiation-sensitive sensorarranged on a first side of the slab, the sensor being an integral partof said slab and being sensitive to the radiation of the projectionbeam; and a film of a material that is non-transparent to the radiationof the projection beam. The film is provided on the first side of theslab over the sensor and has a patterned segment above the sensorconfigured and arranged to selectively pass radiation of the projectionbeam to the sensor. The slab is mounted with a surface opposite to thefirst side facing a slab-bearing surface of an intermediate plate madefrom a material having a thermal expansion coefficient belowapproximately 12×10⁻⁶K⁻¹.

Although specific reference may be made to this text to the use of theapparatus according to the invention in the manufacture of ICs, itshould be explicitly understood that such an apparatus has many otherpossible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid-crystal display panels,thin-film magnetic heads, etc. The skilled artisan will appreciate that,in the context of such alternative applications, any use of the terms“reticle”, “wafer” or “die” in this text should be considered as beingreplaced by the more general terms “mask”, “substrate” and “targetportion”, respectively.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including ultraviolet(UV) radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm)and extreme ultra-violet (EUV) radiation (e.g. having a wavelength inthe range 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 schematically depicts a lithographic projection apparatusaccording to an embodiment of the invention;

FIG. 2 schematically depicts a cross-section of an image sensing devicebeing part of the apparatus of FIG. 1;

FIG. 3 schematically depicts the image sensing device of FIG. 2 mountedon the substrate table shown in FIG. 1;

FIG. 4 shows further details of a sensor being part of the image sensingdevice;

FIG. 5A depicts an embodiment of neighboring image sensor markers aboverespective sensors in the image sensing device;

FIGS. 5B and 5C depict various marks for cooperation with the sensormarks of FIG. 5A;

FIG. 6 depicts two further sets of image sensor marks and neighboringalignment marks;

FIG. 7 depicts a region of the image sensor plate comprising severalsets of image sensor marks and alignment marks;

FIG. 8 depicts a top view of the substrate table holding a substrate andan image sensor plate;

FIG. 9A depicts two image sensor plates according to the invention,which are processed from a six-inch wafer; and

FIG. 9B depicts one image sensor plate according to the invention, whichis processed from one four-inch wafer.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic projection apparatusaccording to a particular embodiment of the invention. The apparatuscomprises:

-   -   A radiation system Ex, IL, for supplying a projection beam PB of        radiation (e.g. UV or EUV radiation). In this particular        example, the radiation system also comprises a radiation source        LA;    -   A first object table (mask table) MT provided with a mask holder        for holding a mask MA (e.g. a reticle), and connected to a first        positioning structure for accurately positioning the mask with        respect to item PL;    -   A second object table (substrate table) WT provided with a        substrate holder for holding a substrate W (e.g. a resist-coated        silicon wafer), and connected to a second positioning structure        for accurately positioning the substrate with respect to item        PL; and    -   A projection system (“lens”) PL (e.g. reflective, a refractive        or a catadioptric lens design) for imaging an irradiated portion        of the mask MA onto a target portion C (e.g. comprising one or        more dies) of the substrate W.

As here depicted, the apparatus is of a reflective type (i.e. has areflective mask). However, in general, it may also be of a transmissivetype, for example (with a transmissive mask). Alternatively, theapparatus may employ another kind of patterning structure, such as aprogrammable mirror array of a type as referred to above.

The source LA (e.g. a mercury lamp, an excimer laser, a laser-producedplasma source or discharge plasma source, or an undulator providedaround the path of an electron beam in a storage ring or synchrotron)produces a beam of radiation. This beam is fed into an illuminationsystem (illuminator) IL, either directly or after having traversed aconditioning structure or field, such as a beam expander Ex, forexample. The illuminator IL may comprise an adjusting structure or fieldAM for setting the outer and/or inner radial extent (commonly referredto as σ-outer and σ-inner, respectively) of the intensity distributionin the beam, which may affect the angular distribution of the radiationenergy delivered by the projection beam at, for example, the substrate.In addition, the apparatus will generally comprise various othercomponents, such as an integrator IN and a condenser CO. In this way,the beam PB impinging on the mask MA has a desired uniformity andintensity distribution in its cross-section.

It should be noted with regard to FIG. 1 that the source LA may bewithin the housing of the lithographic projection apparatus (as is oftenthe case when the source LA is a mercury lamp, for example), but that itmay also be remote from the lithographic projection apparatus, theradiation beam which it produces being led into the apparatus (e.g. withthe aid of suitable direction mirrors); this latter scenario is oftenthe case when the source LA is an excimer laser. The current inventionand claims encompass both of these scenarios.

The beam PB subsequently intercepts the mask MA, which is held on a masktable MT. Having been selectively reflected by the mask MA, the beam PBpasses through the lens PL, which focuses the beam PB onto a targetportion C of the substrate W. With the aid of the second positioningstructure (and interferometric measuring structure IF), the substratetable WT can be moved accurately, e.g. so as to position differenttarget portions C in the path of the beam PB. Similarly, the firstpositioning structure can be used to accurately position the mask MAwith respect to the path of the beam PB, e.g. after mechanical retrievalof the mask MA from a mask library, or during a scan. In general,movement of the object tables MT, WT will be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which are not explicitly depicted in FIG. 1. However, inthe case of a wafer stepper (as opposed to a step-and-scan apparatus)the mask table MT may just be connected to a short stroke actuator, ormay be fixed. Mask MA and substrate W may be aligned using maskalignment marks M1, M2 and substrate alignment marks P1, P2.

The depicted apparatus can be used in two different modes:

-   -   1. In step mode, the mask table MT is kept essentially        stationary, and an entire mask image is projected at once (i.e.        in a single “flash”) onto a target portion C. The substrate        table WT is then shifted in the x and/or y directions so that a        different target portion C can be irradiated by the beam PB;    -   2. In scan mode, essentially the same scenario applies, except        that a given target portion C is not exposed in a single        “flash”. Instead, the mask table MT is movable in a given        direction (the so-called “scan direction”, e.g. the y direction)        with a speed v, so that the projection beam PB is caused to scan        over a mask image; concurrently, the substrate table WT is        simultaneously moved in the same or opposite direction at a        speed V=Mv, in which M is the magnification of the lens PL        (typically, M=¼ or ⅕). In this manner, a relatively large target        portion C can be exposed, without having to compromise on        resolution.

A sensor plate 100 comprising an image sensing device (image sensor) 110is mounted on substrate table WT, the image sensor being used formeasuring the aerial image of a pattern on a mask that is provided onmask table MT. Such a measurement allows determining lens aberrations,lens magnification, and the focus plane of the lens, but also allowsalignment of substrate table WT and mask pattern (mask table MT).

FIG. 2 shows a view of the image sensor in cross-section. In thisexample, the image sensor is based on diode technology. Siliconphotodiodes are semiconductor devices that are responsive to photons.Photons are absorbed and create electron-hole pairs to generate a flowof electrical current in an external electrical circuit, proportional tothe incident power. Photodiodes can be used to detect the presence orvariations in minute quantities of light and can be calibrated forextremely accurate measurements of intensities having a dynamic range ofeleven orders of magnitude.

The image sensor of FIG. 2 is made in a silicon (or anothersemiconducting material such as germanium (Ge), gallium arsenide (GaAs),or gallium nitride) wafer 101 that has been polished on both sides toobtain a required flatness (ultra-flat) and a thickness between 600 and1000 μm. At one side of the wafer (denoted as the front side) a thinlayer 102 of 1 to 10 μm silicon is epitaxially grown, in which layer thediodes 111 are processed at some locations in the wafer by means ofknown semiconductor manufacturing technology techniques including e.g.lithographic projection and ion implantation techniques. A diode isshown only schematically in FIG. 2. Electronic contacts 120 to thediodes are processed from the other side of the wafer (denoted as theback side). The contacts may be established by etching holes in the backside, which pass through the wafer to the ion implanted regions 112 ofthe diode at the front side. In this case, the etched holes may befilled with tungsten, which is electrically conducting. The tungstenpillars are electrically connected to larger bond flaps 121 at the backside of the wafer, which are to be connected to processing electronics.In another embodiment, the etched holes are left open at this stage. Atsome later stage they may be completely or partially (only on the walls,for instance) filled with a conductive glue when being mounted on anintermediate base plate, for instance.

The front surface of the wafer, in which the diodes were processed, iscovered with a protective layer 103. For instance, it may be desirablefor this layer to act as a plasma etch stop. In this example, layer 103is a 10 to 20 nm thick layer of silicon nitride (Si₃N₄). Subsequently, a50 to 100 nm thick metal layer 104 is sputtered on top of the siliconnitride layer. Marker patterns 113 are plasma-etched in the metal layerabove the silicon diodes 111 (e.g. using known lithographic projectiontechniques) to define the marker patterns. The patterned metal layerabove the photodiodes selectively passes EUV radiation to the photodiodeaccording to the pattern in the metal layer.

In a further embodiment, an additional zirconium (Zr) layer in the orderof 100 nm may be provided over the diodes, for instance, directly belowlayer 103 in the embodiment shown. One possible advantage of such azirconium layer is effective blockage of deep ultraviolet and visibleradiation, with passage in the order of 70% of the incident EUVradiation to the underlying diodes, such that the blocked radiation willnot decrease the dynamic range and signal-to-noise ratio of the sensoror otherwise affect detection of an aerial image of EUV radiation.

Sensor plate 100 comprises a major part of a silicon wafer in whichseveral photodiodes covered by marker patterns are provided. FIG. 3shows that the image sensor plate 100 is carried by the upper surface ofan intermediate base plate 200 to provide stability of the sensor plateand to also carry processing electronics 300 for the image sensor. Bothupper and lower surfaces of the base plate are polished, the uppersurface being polished to ultra-flat specifications. Image sensor andbase plates are mounted together on substrate table WT. It may bedesirable to fashion the base plate from a low thermal expansionmaterial like a glass ceramic material (being a glass with someadditional ceramic to yield favourable properties) such as Zerodure™ (amaterial available from Schott glass, Hattenbergstrasse 10, 55120,Mainz, Germany) and ULE™ (a material available from CorningIncorporated, 1 River Front Plaza, Corning, N.Y. 14831), or a glass suchas quartz, presenting a coefficient of thermal expansion below12×10⁻⁶K⁻¹. A sensor plate of low thermal expansion material is alsocontemplated.

A glue or other adhesive may be used to mount the image sensor plate 100on the base plate 200 as shown in the left-hand part of FIG. 3. For suchpurpose, grooves 210 may be provided in the top surface for containing aglue 130 that pulls the sensor plate against the base plate aftershrinkage. The sensor plate may also be attached to the base plate bydirect bonding (being physical attraction between two very flatsurfaces), which may provide a better overall flatness of the front sideof the sensor plate 100. An embodiment adapted for direct bondingprovides for a silicon dioxide layer (for instance, between 10 and 1000nm thick) at the back side of the sensor plate for direct bonding to aquartz base plate, since the physical properties of the silicon dioxidelayer resemble those of the quartz base plate. General requirements fordirect bonding are a good cleanliness and good flatness of thecontacting surfaces. In case of direct bonding, a very flat surface willbe presented to the sensor plate for its support.

A cavity 220 is provided in the base plate for mounting an electroniccircuitry plate 300 that comprises pre-amplifying electronics for theimage sensor. In one implementation, the base plate is 6 mm thick andthe cavity is 3 mm deep. Holes are drilled through the base plate toallow for electrical connections between sensor plate and electroniccircuitry plate. The holes may be filled with some conductive glue (suchas an epoxy) that contacts respective bond flaps of the sensor plate andthe electronic circuitry plate after assembling the whole unit. One mayalso provide rods 230 (gold rods or gold-plated steel rods, forinstance) through the holes that are connected to their respective bondflaps using a conductive glue. The electronic circuitry plate 300 may bemounted in various manners in its cavity in the base plate, forinstance, using a silicone gel. Generally, the sensor plate will bemounted first on the base plate, followed by providing electricalconnections through the holes in the base plate and mounting theelectronic circuitry plate. From the electronic circuitry plate, furtherelectric connections may be provided to further processing electronicselsewhere in the system.

It may be desirable to mount the base plate 200 in some removable manneron the substrate table WT, for instance, by a magnetic coupling bymagnets 250, so that it can be removed for maintenance purposes. Asubstrate may be held on the substrate table by using a double-sidedelectrostatic chuck, which provides for attraction of a substrate to thechuck and of the chuck to the substrate table for holding of thesubstrate under vacuum conditions. The top side surface of sensor plate100 is preferably in the same plane, or as close as possible, to the topside surface plane of the substrate. Chucks of various types andthickness may be employed for this purpose. Spacer plates 260 in betweenbase plate and substrate table can be used to have the thickness of thesensor plate and base plate assembly adjusted accordingly. Such spacersare preferably provided around magnets 250 for holding the base plate onthe substrate table and may also be attached to the base plate by directbonding.

To shield the electronics inside cavity 220 and the electricalconnections through base plate 200 from external electromagneticinfluences (for instance, electromagnetic radiation present due tooperation of an EUV plasma source), the base plate is preferably coveredwholly or in part by a sufficiently thick metal layer 201. For mostmetals, a layer thickness in the order of 1 μm is sufficient forblocking radio frequency electromagnetic radiation in the 1 Hz to 1 GHzrange. The metal layer may be provided, for example, by sputtering onthe exterior surface of the base plate. Chromium is a preferred metalbecause of its high electrical conductivity, low oxidation and highsputtered layer quality.

In case the sensor plate is attached to the base plate by directbonding, it should be prevented that the metal layer 201 is provided onthat part of the base plate surface onto which the sensor plate is to bedirectly bonded at a later stage. To this end a dummy sensor plate maybe positioned on the base plate while providing metal layer 201. Asilicon wafer having a silicon nitride (Si₃N₄) skin layer may be usedfor this purpose, since it ensures easy removal of the dummy plate and auniform direct bonding. The dummy plate can be removed by moderatemechanical force or using a nonpolar fluid. After attaching of sensorplate 100 to the non-covered area of base plate 200 an electricalconnection between sensor plate and metal layer 201 is provided, forinstance, by an electrical conductive glue around the perimeter of thesensor plate. Layer 201 is connected to, for instance, ground potentialwhen the whole assembly is mounted on the substrate table WT. A cleararea should also be provided for spacer plates in case such plates areto be attached to the base plate by direct bonding.

FIG. 4 shows in more detail a cross-section of one example of a photodiode as processed in a wafer for detecting EUV radiation. A p-typeepitaxially grown silicon layer 102 is grown on a p-type substrate(silicon wafer) 101. N-type regions 105 are provided at sides of adefect-free n-type region 106 in the epitaxial layer 102, as well asp-type regions 107. A field oxide 108 covers the n-type and p-typeregions and electrical connects 120 are provided in contact with then-type and p-type regions. A platinum silicide or titanium silicidelayer 109 a few nanometers thick is provided over the defect-free n-typeregion 106 on which radiation should be incident for detection purposes.The patterned area 113 in the metal layer 104 is provided abovedefect-free n-type region 106.

For aerial image sensing purposes several photo diodes are provided onthe sensor plate 100, each having its own pattern provided in the metallayer on top. FIG. 5A shows a series of four neighboring image sensormark patterns, each provided above its respective photo diode. Eachpattern fills a square of 200 μm×200 μm, for instance, and the patterns(and respective diodes) are approximately 200 μm apart, for instance.The series contains a −45° mark 413, an X direction mark 411, a Ydirection mark 412 and +45° mark 414, respectively. The patterns aregratings having a certain pitch and line width and having their linesoriented as shown in the figure. The widths of the transmissivestructures (referred to as groove widths or line widths in thisspecification) are in the order of 100 nm (for instance, between 30 and300 nm), and the pitch may be in the order of 1 μm (for instance,between 0.3 and 9 μm).

FIGS. 5B and 5C show two series of mask mark patterns for cooperationwith the series of sensor mark patterns of FIG. 5A. The series of FIG.5B contains a ratio mark 420, an X direction mark 421, a Y directionmark 422 and a ratio mark 420, respectively, while the series of FIG. 5Ccontains a −45° mark 423, two ratio marks 420 and a +45′ mark 424,respectively. The marks are again gratings, as above, except for theratio marks, which are areas of constant reflection provided on themask. They may be fully reflective or 50% reflective, for instance. Eachfirst mark of a series of mask marks is imaged onto the first mark ofthe series of sensor marks, each second mask mark onto the second sensormark, etc. Outer dimensions of the mask marks are chosen such that animage of a mask mark will generally be larger or smaller than itscorresponding image sensor mark to allow for a relative scanningmovement of mask and image sensor marks. However, dimensions of pitchand line width of an image of a mask mark will generally correspond toits respective image sensor mark (taking lens magnification and/ordemagnification into account).

Marks as shown have a constant pitch and line width across the mark. Ingeneral, however, pitch and line width may vary across a mark. In oneexample, triplets of lines (also referred to as grooves in the contextof this specification) are presented, the lines in a triplet havingdifferent line widths, for instance. Further, one may have equal linewidth across a mark and a varying pitch, for instance, for each tripletof lines (grooves) for additional functionality, or both have varyingline width and varying pitch across the mark.

Scanning in the X and Y direction and imaging the series of mask marksof FIG. 5B onto the series of sensor marks of FIG. 5A yields aerialimage information for the X direction and Y direction marks, while forthe +45° and −45° direction marks this operation yields uniformintensity distributions that support ratio sensing by the respectivephoto diodes. Signals detected by the ratio sensors are used fornormalizing the signals yielded by the gratings and their respectivephoto diodes to correct for source fluctuations. The series of FIG. 5Cyields aerial image information on the 45° directions.

Outer dimensions of the ratio mask marks 420 are shown to be identicalto the outer dimensions of the grating mask marks (taking lensmagnification and/or demagnification into account). However, in anothercase the dimensions of one of the ratio mask marks may be chosen suchthat it will underfill its respective image sensor mark, while thedimensions of the other ratio mask mark are chosen such it will overfillits respective image sensor mark for coarse capturing schemes whilescanning. Scanning then yields the position of the small ratio mark spotwithin the capture range of its respective image sensor mark, while thecorresponding signal can be corrected for source fluctuations using thesignal of the overfilled image sensor mark.

FIG. 6 shows two alternative series of image sensor marks, the upper setcomprising a ratio mark 410, an Y direction mark 412, and X directionmark 411 and another ratio mark 410, respectively, while the lowerseries comprises a ratio mark 410, a −45° mark 413, a +45′ mark 414 andanother ratio mark 410, respectively. The transmissive surface area ofthe square of ratio marks 410 equals the transmissive surface area of Xand Y direction marks 411, 412 and of the −45′ and +45° marks 413, 414.The series of mask marks to be used with these series of image sensormarks reflect the configuration of the series of image sensor marks.This embodiment presents two series of image sensor marks to yield X, Y,−45° and +45° information, while the previous embodiment only requiredone series. The considerations with regard to the dimensions of themarks are identical as set out above. FIG. 6 also shows the outerdimensions of the photodiodes underlying the mark patterns in phantom.

However, it may be advantageous to have ratio marks taking the form ofgratings over the photo diodes, which have groove widths (also beingreferred to as line widths in this specification) equal to the linewidths of the neighboring image sensor mark patterns, to have the samespectral sensitivity for both ratio sensor and image sensor. It may evenbe further preferred for those gratings in the same direction to alsohave an equal polarization dependency. Pitches may vary between imagesensor and corresponding ratio sensor.

Returning again to FIG. 6, it also shows two alignment marks 450 to beused to align a substrate W present on the substrate table WT withrespect to the substrate table. To this end alignment marks are providedon both the substrate WT and on the image sensor plate 100. An alignmentmodule allows for aligning the alignment marks with regard to areference using an alignment beam of radiation, while reading thecorresponding positions of the substrate table using the interferometricmeasuring structure IF. When the substrate table has been aligned withrespect to the mask using the image sensor, the position of thesubstrate with respect to the mask is now also known. In the embodimentshown, the alignment marks are phase marks that are provided in thefront side of the sensor plate employing lithographic projection andmanufacturing techniques, such as etching. Such techniques allowprocessing of alignment and image sensor marks with a high accuracy withrespect to each other, which quality may be highly advantageous withrespect to an operation of correctly positioning a substrate withrespect to a pattern in a mask.

Multiple sets of image sensor marks, ratio marks, underlying photodiodes and alignment marks may be provided on the sensor plate. Each setof marks may be designed for specific purposes and/or measurements. FIG.7 depicts multiple sets corresponding to the ones of FIG. 6 present onthe sensor plate.

FIG. 8 shows a top view of one example of substrate table WT on which asubstrate W is located. In this example, sensor plate 100 is located ina corner of the substrate table next to the substrate position.Optionally, another sensor plate may be located in another corner of thesubstrate table, and/or other kinds of sensors may be located in one ormore other corners.

FIGS. 9A and 9B shows how sensor plates 100 may be cut from a six-inchwafer and a four-inch wafer, respectively. In the areas shown inphantom, the image sensors and marks as discussed above are processedusing semiconductor manufacturing techniques. The reflective area mayalso be used by a level sensor (not shown) to determine height and tiltof the substrate table.

The image sensor and ratio sensor as described above may also be usedfor measuring the intensity of the projection beam, e.g. for control ofthe dose of radiation incident on the substrate in the imaging process.However, the sensors may become polluted over time, predominantly by an(amorphous) carbon layer due to hydrocarbon molecules cracked under EUVradiation. Carbon shows a high absorption of EUV radiation: for example,1% of incident EUV radiation may be absorbed by a 0.5 nm thick carbonlayer. The presence of a carbon layer of unknown thickness may interferewith the use of the image (and/or ratio) sensor for calibrated EUV dosemeasurements. In such case, visible light (or even infrared radiation)may be used to accurately measure the carbon layer thickness, e.g. tosupport correction for absorbed EUV radiation. One possible advantage ofsuch an operation is to avoid cleaning of the sensors at short timeintervals.

It is shown that radiation between 400 and 1100 nm may, to some extent,penetrate into grooves having a width in the order of 100 nm in case theradiation is polarized perpendicular to the grooves (TM polarization, asopposed to TE polarization). Such radiation will be the mark structuresabove the photo diodes, as described above, and will be detected by thephotodiodes, which are sensitive to radiation above 400 nm.

It has further been shown that that radiation in the range of 400 to1100 nm is readily absorbed by an (amorphous) carbon layer (absorptionis even higher than for EUV radiation) and a carbon layer thickness canbe accurately determined. Part of the beam of radiation in the range of400-1100 nm can be split off using a beam splitter and be directed to areference detector to correct for intensity fluctuations. EUV radiationwould not be incident on such a reference sensor, and will therefore notcause carbon build-up on the reference sensor due to cracking ofhydrocarbons by incident EUV radiation. The reference sensor willtherefore remain clean. In case of a very stable light source, one mightcontemplate not employing a reference branch and not to employ TMpolarized radiation.

Whilst specific embodiments of the invention have been described above,it will be appreciated that the invention as claimed below may bepracticed otherwise than as described. It is explicitly noted that thedescription of these embodiments is not intended to limit the inventionas claimed.

1. A lithographic apparatus configured and arranged to image a patternonto a substrate that is at least partially covered by a layer ofradiation-sensitive material, said apparatus comprising: an imagesensing device configured and arranged to measure a pattern in apatterned beam of radiation, said image sensing device including: aslab; at least two radiation-sensitive sensors arranged at a first sideof the slab, each sensor being formed on said slab and being sensitiveto the radiation of the beam; and a film of a material that isnon-transparent to the radiation of the beam, said film being providedat the first side of the slab over said sensors and including apatterned segment above each sensor configured and arranged toselectively pass radiation of the beam to said sensor.
 2. Thelithographic apparatus according to claim 1, wherein at least one of thepatterned segments comprises sets of grooves, each set having a separatepitch.
 3. The lithographic apparatus according to claim 1, wherein atleast one of said patterned segments above said sensors comprises aplurality of transmissive areas configured to pass radiation of thebeam.
 4. The lithographic apparatus according to claim 3, wherein thetransmissive areas within each of said at least one patterned segmentare at least substantially equally oriented.
 5. The lithographicapparatus according to claim 3, wherein a width of each of saidtransmissive areas is in the range of 30 to 300 nm.
 6. The lithographicapparatus according to claim 3, wherein within each of said at least onepatterned segment a width of the transmissive areas is at leastsubstantially equal.
 7. The lithographic apparatus according to claim 3,wherein within each of said at least one patterned segment a pitch ofsaid plurality of transmissive areas is in the range of fromthree-tenths (0.3) microns to nine (9) microns.
 8. The lithographicapparatus according to claim 7, wherein the integrated surface areas ofthe at least one transmissive area for each respective patterned segmentare substantially in the same order of magnitude.
 9. The lithographicapparatus according to claim 1, wherein each of said patterned segmentsabove said sensors comprises at least one transmissive area configuredto pass radiation of the beam.
 10. The lithographic apparatus accordingto claim 9, wherein at least one of said patterned segments comprises aplurality of transmissive areas, and wherein within each of said atleast one patterned segment a width of the transmissive areas is atleast substantially equal.
 11. The lithographic apparatus according toclaim 9, wherein at least one of said patterned segments comprises aplurality of transmissive areas, and wherein within each of said atleast one patterned segment said transmissive areas are at leastsubstantially equally oriented.
 12. The lithographic apparatus accordingto claim 9, wherein the integrated surface areas of the at least onetransmissive area for each patterned segment are substantially of thesame order of magnitude.
 13. The lithographic apparatus according toclaim 9, wherein at least one of said patterned segments comprises aplurality of transmissive areas, and wherein within each of said atleast one patterned segment a width of each of said transmissive areasis in the range of 30 to 300 nm.
 14. The lithographic apparatusaccording to claim 9, wherein each of said patterned segments has asubstantially square shape.
 15. The lithographic apparatus according toclaim 9, wherein a pitch of said patterned segments is substantiallyequal to two hundred (200) microns.
 16. The lithographic apparatusaccording to claim 9, wherein at least one of said transmissive areas atleast substantially surrounds a non-transparent area.
 17. Thelithographic apparatus according to claim 9, wherein a first one of saidpatterned segments comprises a transmissive area that at leastsubstantially surrounds a non-transmissive area, and wherein a secondone of said patterned segments comprises a plurality of transmissiveareas, and wherein the integrated surface areas of the transmissiveareas for the first patterned segment and for the second patternedsegment are substantially of the same order of magnitude.
 18. Thelithographic apparatus according to claim 1, wherein said first side ofsaid slab is substantially coplanar with a surface of the substrate thatis at least partially covered by the layer of radiation-sensitivematerial.
 19. The lithographic apparatus according to claim 1, whereinat least one of said sensors is substantially covered at the first sideby a layer comprising zirconium.
 20. The lithographic apparatusaccording to claim 1, wherein at least one of a surface of the slabadjacent to the first side and a surface of the slab opposite to thefirst side is polished.
 21. The lithographic apparatus according toclaim 1, wherein electrical connections to said at least tworadiation-sensitive sensors are provided through said slab from asurface opposite to the first side of said slab.
 22. The lithographicapparatus according to claim 21, wherein said electrical connectionscomprise metal-filled contact holes provided through said slab from thesurface opposite to the first side of said slab.
 23. The lithographicapparatus according to claim 21, wherein a surface of the slab oppositeto the first side is provided with electrical contact pads conductivelyconnected to said electrical connections.
 24. The lithographic apparatusaccording to claim 1, wherein the slab comprises a wafer ofsemiconductor material on which said at least two radiation-sensitivesensors are fabricated.
 25. The lithographic apparatus according toclaim 24, wherein said semiconductor material comprises silicon.
 26. Thelithographic apparatus according to claim 1, wherein at least one ofsaid radiation-sensitive sensors is a diode.
 27. The lithographicapparatus according to claim 1, wherein the beam of radiation comprisesradiation having a wavelength in the range from five to twentynanometers.
 28. The lithographic apparatus according to claim 1, whereinat least one of said patterned segments above said sensors comprises aplurality of transmissive areas configured to pass radiation of thebeam, and wherein at least one of a pitch and a line width of saidtransmissive areas varies within at least one of said patternedsegments.
 29. The lithographic apparatus according to claim 1, saidapparatus comprising: a radiation system configured and arranged toprovide a beam of radiation; a support structure configured and arrangedto support a patterning structure, the patterning structure serving toproduce a desired pattern in the beam of radiation; a substrate tableconfigured and arranged to hold the substrate; and a projection systemconfigured and arranged to project the patterned beam onto a targetportion of the substrate.
 30. The lithographic apparatus according toclaim 1, wherein a distance between a pair of said at least tworadiation-sensitive sensors is less than the thickness of the slab. 31.The lithographic apparatus according to claim 1, wherein a distancebetween a pair of said at least two radiation-sensitive sensors is lessthan one-half of the thickness of the slab.
 32. A lithographic apparatusconfigured and arranged to image a pattern onto a substrate that is atleast partially covered by a layer of radiation-sensitive material, saidapparatus comprising: a substrate table configured and arranged to holdthe substrate; an image sensing device configured and arranged tomeasure a pattern in a patterned beam of radiation, said image sensingdevice including: a slab; at least two radiation-sensitive sensorsarranged at a first side of the slab, each sensor being formed on saidslab and being sensitive to the radiation of the beam; a film of amaterial that is non-transparent to the radiation of the beam, said filmbeing provided at the first side of the slab over said sensors andincluding a patterned segment above each sensor configured and arrangedto selectively pass radiation of the beam to said sensor; and anintermediate plate disposed between the substrate table and the slab,wherein said slab is mounted with a surface opposite to the first sidefacing a first surface of the intermediate plate.
 33. The lithographicapparatus according to claim 32, said apparatus comprising spacer platesarranged to adjust a position of the first side of the slab.
 34. Thelithographic apparatus according to claim 32, said apparatus comprisingat least one magnet arranged to hold the intermediate plate on thesubstrate table.
 35. The lithographic apparatus according to claim 32,wherein said intermediate plate is made from at least one among a glassand a glass ceramic material.
 36. The lithographic apparatus accordingto claim 35, wherein said intermediate plate is made from at least oneamong ULE™, Zerodur™ and quartz.
 37. The lithographic apparatusaccording to claim 32, wherein the first surface of said intermediateplate is polished.
 38. The lithographic apparatus according to claim 32,wherein said slab is attached to said intermediate plate by directbonding.
 39. The lithographic apparatus according to claim 32, whereinelectrical connections are provided from a surface of the slab oppositeto the first side of said slab through said intermediate plate.
 40. Thelithographic apparatus according to claim 32, wherein a portion of theexterior of said intermediate plate is covered by a conductive layer.41. The lithographic apparatus according to claim 32, wherein a distancebetween a pair of said at least two radiation-sensitive sensors is lessthan the thickness of the slab.
 42. The lithographic apparatus accordingto claim 32, wherein a distance between a pair of said at least tworadiation-sensitive sensors is less than one-half of the thickness ofthe slab.
 43. A device manufacturing method including imaging a patternonto a substrate that is at least partially covered by a layer ofradiation-sensitive material, said method comprising: using patterningstructure to endow a beam of radiation with a pattern in itscross-section; measuring a pattern in the patterned beam using an imagesensing device that includes a slab having at least tworadiation-sensitive sensors arranged on a first side of the slab, eachsensor being formed on said slab and being sensitive to the radiation ofthe beam, wherein said measuring comprises using at least one of saidsensors to measure an intensity of an unpatterned area in across-section of said patterned beam, and using at least another one ofsaid sensors to measure an intensity of a patterned area neighboring theunpatterned area in the cross-section of said patterned beam.
 44. Adevice manufactured according to the device manufacturing method ofclaim
 43. 45. The device manufacturing method according to claim 43,wherein the image sensing device comprises a film of material that isnon-transparent to the radiation of the projection beam, is provided onthe first side of the slab over said sensors, and includes a patternedsegment above each sensor configured and arranged to selectively passradiation of the beam to said sensor.
 46. The device manufacturingmethod according to claim 45, wherein the patterned segment above the atleast one of said sensors used to measure an intensity of an unpatternedarea in a cross-section of said patterned beam comprises a transmissivearea that substantially surrounds a square non-transmissive area. 47.The device manufacturing method according to claim 43, wherein at leastone of said sensors configured and arranged to measure an intensity ofthe unpatterned area has an outer dimension substantially equal to thatof the unpatterned area in the cross-section of the projection beam. 48.The device manufacturing method according to claim 43, wherein saidmeasuring includes using another of said sensors to measure an intensityof another unpatterned area in a cross-section of said patternedprojection beam.
 49. The device manufacturing method according to claim48, wherein at least one of said sensors used to measure an intensity ofone of the unpatterned areas has an outer dimension greater than that ofthe corresponding unpatterned area in the cross-section of theprojection beam, and wherein another of said sensors used to measure anintensity of another of the unpatterned areas has an outer dimensionsmaller than that of the corresponding unpatterned area in thecross-section of the projection beam.
 50. The device manufacturingmethod according to claim 43, said method comprising projecting thepatterned beam of radiation onto the image sensing device, wherein saidprojecting includes scanning the unpatterned area of the patterned beamover the at least one of said sensors used to measure an intensity of anunpatterned area in a cross-section of the patterned beam and scanningthe patterned area of the patterned beam over the at least another oneof said sensors used to measure an intensity of a patterned area in across-section of the patterned beam.
 51. The device manufacturing methodaccording to claim 50, wherein said projecting the patterned beam ofradiation onto the image sensing device includes using a projectionsystem to project the patterned beam of radiation, said methodcomprising using the projection system to project a patterned beam ofradiation onto a target portion of the layer of radiation-sensitivematerial.
 52. The device manufacturing method according to claim 43,wherein said image sensing device is mounted on a substrate table thatholds the substrate, said method comprising determining, based on atleast one alignment mark arranged at the first side of the slab, aposition of the substrate table with respect to a reference.
 53. Thedevice manufacturing method according to claim 43, said methodcomprising measuring a thickness of a layer of carbon over at least oneof said sensors.
 54. The device manufacturing method according to claim43, wherein a distance between a pair of said at least tworadiation-sensitive sensors is less than the thickness of the slab. 55.The device manufacturing method according to claim 43, wherein adistance between a pair of said at least two radiation-sensitive sensorsis less than one-half of the thickness of the slab.